With the development of radio and space technologies, several satellites based navigation systems (i.e. satellite positioning system or “SPS”) have already been built and more will be in use in the near future. Those systems with full global coverage are sometimes referred to as Global Navigation Satellite Systems (“GNSS”). SPS receivers, such as, for example, receivers using the Global Positioning System (“GPS”), also known as NAVSTAR, have become commonplace. Other examples of SPS and/or GNSS include but are not limited to the United States (“U.S.”) Navy Navigation Satellite System (“NNSS”) (also known as TRANSIT), LORAN, Shoran, Decca, TACAN, the Russian counterpart to NAVSTAR known as the Global Navigation Satellite System (“GLONASS”), any future Western European SPS such as the proposed “Galileo” program, or any other existing or future system such as the Chinese “Beidou” or “Compass” system. As an example, the U.S. NAVSTAR GPS system is described in GPS Theory and Practice, Fifth ed., revised edition by Hofmann-Wellenhof, Lichtenegger and Collins, Springer-Verlag Wien New York, 2001.
The U.S. GPS system was built and is operated by the United States Department of Defense. The system uses twenty-four or more satellites orbiting the earth at an altitude of about 11,000 miles with a period of about twelve hours. These satellites are placed in six different orbits such that at any time a minimum of six satellites are visible at any location on the surface of the earth except in the polar region. Each satellite transmits a time and position signal referenced to an atomic clock. A typical GPS receiver locks onto this signal and extracts the data contained in it. Using signals from a sufficient number of satellites, a GPS receiver can calculate its position, velocity, altitude, and time.
In the location/positioning industry, there are more and more demands for multi-system receivers instead of receivers that only supports the legacy navigation system), such as, GPS. However, it is very difficult to make a legacy GPS receiver to support multiple navigation satellite systems without significant hardware change, as most of the GPS receivers use the hardware correlator design and can not process other navigation satellite system signals without modifying the hardware. In addition, different systems use different modulation formats. For example, GLONASS uses Frequency Division Multiple Access (FDMA) scheme for signal communication, which is totally different from the Code Division Multiple Access (CDMA) scheme used by GPS and the Galileo systems. Therefore, processing of multiple types of communication signal becomes more dependant on hardware modification to support multi-system functionality.
It will be desirable to enable a legacy receiver to process satellite signals coming from satellites belonging to different types of GNSS. However, it is desirable to accomplish that via software upgrade, without having to redesign the hardware. The inventors are not aware of any software-based solution that is currently available to implement a multi-GNSS receiver.